2 research outputs found

    Synthesis of Nanoscale Heterostructures Comprised of Metal Nanowires, Carbon Nanotubes, and Metal Nanoparticles: Investigation of Their Structure and Electrochemical Properties

    Get PDF
    One-dimensional nanoscale heterostructures comprised of multisegment gold-nickel nanowires, carbon nanotube, and nickel nanoparticles were fabricated in a unique approach combining top-down and bottom-up assembly methods. Porous alumina template was utilized for sequential electrodeposition of gold and nickel nanowire segments. This was followed by chemical vapor deposition growth of carbon nanotubes on multisegment gold-nickel nanowires, where nickel segment also acted as a carbon nanotube growth catalyst. The aligned arrays of these gold-nickel-carbon nanotube heterostructures were released from porous alumina template and then subjected to wet-chemical process to be decorated with nickel/nickel oxide core/shell nanoparticles. X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and Raman spectroscopy were utilized for morphology, interface, defect, and structure characterization. The electrochemical performance of these heterostructures was studied using cyclic voltammetry method and the specific capacitance of various heterostructures was estimated and compared

    From Design to Orbit: Engineering Sub-Arcsecond CubeSat Pointing Performance on Pathfinder-3

    Get PDF
    Pathfinder-3 (PTD-3) spacecraft is the third vehicle of the NASA Pathfinder Technology Demonstrator (PTD) series, which are a collection of 6U CubeSats launched in Low Earth Orbit (LEO) to demonstrate innovative payload capabilities. The payloads are hosted on commercially developed satellites designed and manufactured by Terran Orbital Corporation (TOC) with a goal to support a wide array of technology demonstration missions through a flexible architecture that can be tailored for custom needs. PTD-3 hosts a high data rate laser communications payload that does not include its own pointing acquisition and control system, and, therefore, is dependent on accurate bus pointing to establish and maintain the space-to-ground (S2G) link for optical communication transmission. Traditional CubeSat attitude control sensors (i.e. star trackers, gyros) are too coarse to achieve the pointing accuracy and bias requirements of less than 6.2 arcsec (30 µrad) and 3.1 arcsec (15 µrad), respectively. Thus, direct measurements of line-of-sight error from the laser communication payload is provided as feedback into the bus attitude control loop to achieve the pointing accuracy required for the mission. Standard bus attitude control without payload feedback, using star trackers, gyros, and reaction wheels, is implemented to achieve initial acquisition of the ground optical terminal. After acquisition, payload line-of-sight error measurements serve as the source of attitude control feedback for the bus to achieve finer pointing accuracy. This paper presents the design of the spacecraft with a focus on the pointing control architecture, design drivers, preliminary performance predications, and performance evaluation of the on-orbit system. Key design and analysis topics impacting pointing performance centralized around payload-to-bus frame misalignments (both thermal and mechanical), high frequency-induced reaction wheel jitter in the presence of spacecraft flexible modes and mitigation strategies, reaction wheel zero crossings, and the role of TLE induced ephemeris propagation error. The discussion concludes with demonstrations of on-orbit pointing accuracy achieving approximately 0.75 arcsec (4.0 µrad) when payload feedback is in the loop. To the authors’ knowledge, this is among the best CubeSat demonstrated bus pointing achieved while ground tracking. The sub-arcsecond accuracy is accomplished via a low-cost CubeSat architecture (no multi-stage pointing loops with gimbals, fine steering mirrors, etc.) that can be immediately applied to support other similar laser communication systems or observation payloads capable of providing the spacecraft with low noise small angle attitude error measurements
    corecore